The present invention relates to novel porphyrin compounds and methods for making these compounds. More specifically, the novel compounds of the present invention are .beta.-octafluoro-meso-tetraarylporphyrins and their metallic complexes.
Porphyrins are derivatives of porphinc, a conjugated cyclic structure of four pyrrole rings linked through their 2- and 5-positions by methine bridges. The following is the structure of an unsubstituted porphyrin with its .beta. and meso positions labeled: ##STR2## While iron, manganese and chromium unsubstituted porphyrin derivatives are known to be effective oxidation catalysts, the main disadvantage of using these porphyrins as catalysts is that they undergo oxidative degradation under the strong oxidizing conditions of the reaction being performed. Thus, the short lifetime of these porphyrin derivative catalysts lowers their catalytic efficiency.
To help stabilize these porphyrin catalysts, electron-withdrawing groups, such as aryl groups including chlorine or fluorine substituted aryl groups, have been added at the meso positions of the porphyrin. These modifications serve two purposes: 1) The electron-withdrawing effect of the electronegative atoms stabilizes the macrocycle against oxidation; and 2) The steric bulk of these substituents protects the most sensitive (meso) position of the porphyrin ring. Such steric bulk somewhat helps to suppress the formation of catalytically inactive .mu.-oxo dimers of the porphyrins. Still further, placing electron-withdrawing groups at the meso positions creates metalloporphyrins containing a more electrophilic metal. However, metalloporphyrins having bulky substituents at the meso positions are still not sufficiently robust to resist self-oxidation. Oxidation reactions employing these metalloporphyrins as catalysts eventually destroy the metalloporphyrins. Thus, low yields of products are obtained in hydroxylation reactions which use such catalysts.
Still another class of porphyrin catalysts has been created in which electron-withdrawing groups, such as halogens, occupy all of the .beta. positions of the pyrrole rings of the porphyrin. Specifically, porphyrin ligands having bromine and chlorine electron-withdrawing groups at the .beta. positions have been created. The presence of such strong electron-withdrawing groups causes the metal in the metallic porphyrin complexes to be electrophilic in nature. Also, having large atoms such as bromine and chlorine as substituents induces non-planar distortions in the porphyrin; specifically, such atoms cause the porphyrin to adopt a saddle shape. Both the structure and the electrophilic nature of the metalloporphyrins may contribute to the effectiveness of these oxidation catalysts. However, it is difficult to determine whether the catalytic effect of these porphyrins is due to their electronic and/or steric properties since they cannot be isolated from one another so as to determine the contributing effects of each to the catalysis.
Still further, some have disclosed that .beta.-octafluoro-meso-tetraarylporphyrins have been created. However, the methods disclosed for preparing such compounds do not produce such compounds. Furthermore, the characterizing data for such compounds is incorrect and in disagreement with the results of the present invention.
Better oxidation catalysts, which are resistant to degradation and which are capable of having a variety of structural motifs, are needed. Further, catalysts are needed which have electronic and steric effects that can be varied independently. Still further, methods for making such catalysts by making certain porphyrins and their metallic complexes are needed. Especially, a method for making difluoropyrrole, one of the components used to form .beta.-octafluoro-meso-tetraarylporphyrins is needed.